Quaternary salts of chloramphenicol esters of amino acids



United States Patent gan No Drawing. Filed Aug. 11, 1958, Ser. No. 754,180 11 Claims. (Cl. 260-459) The present invention is concerned with quaternary ammonium salts related to threo-l-p-nitrophenyl-Z-dichloroacetamidopropane-l,3!diol esters and to methods for producing the same.

The compounds of the present invention can be represented by the structural formula om-Qonon-hrmomo o 0 011m (lower alkyDsA' Three form where A- is a non-toxic anion. The term non-toxic anion is used to designate those anions normally associated with quaternary ammonium compounds such as the anions of such inorganic acids as hydrochloric, hydrobromic, hydroiodic, sulfuric, phosphoric, and the like. The lower alkyl groups present in the products of the invention can be the same or different and are preferably methyl or ethyl groups.

It will be apparent to those skilled in the art that the 1-pnitrophenyl- 2 dichloroacetamidopropane-l,3-diols used as starting materials in the practice of this invention, as well as the esters of the foregoing structural formula obtained as products therefrom, can exist in various isomeric forms. These include diastereoisomeric forms as well as optically isomeric forms. The present invention is concerned with compounds having the threo diastereoisomeric form as distinguished from the erythro diastereoisomeric form. The groups on the two asymmetric carbon atoms of the threo forms have the same relative spatial configuration or arrangement as the groups on the two asymmetric carbon atoms of pseudo ephedrine and threose. As used herein, the term threo without an accompanying designation of optical form is defined to include DL-threo, corresponding to racemic or DL- threose, and D-threo, corresponding to D-threose. Where a particular optical form is intended, a notation will be used with the term threo such as D-threo.

Because of the difliculty of representing these spatial distinctions in two-dimensional formulas, the customary structural formulas are used throughout the disclosure along with a notation, where appropriate, to designate the stereochemical form.

In accordance with the invention, a haloacetoxy ester of the formula NHOOCHCI:

olN--onon-hnonio o o ontx Three form where X represents a halogen such as chlorine, bromine or iodine; is reacted with a trialkylamine of the formula (lower alkyl) N thereby producing a quaternary ammonium compound of the formula,

. NBC 0 CHCh l om-Qouou-on-omococnm flower alkylla-X 3,000,922 Patented Sept. 19, 1961 ice The reaction of the haloacetoxy ester with the trialkylamine is preferably carried out in solution. The reaction proceeds readily and it, in general, is therefore not necessary to use high temperatures. As a matter of economics, an excess of the trialkylamine is usually employed in order to insure complete utilization of the more expensive haloacetoxy ester compound. As solvents for the reaction, water-miscible organic solvents such as acetonitrile, dioxane, dimethylformamide, dimethylacetamide, and tetrahydrofuran or water-immiscible organic solvents such as chloroform, toluene and benzene may be used. The desired product can be isolated from the reaction mixture in a number of ways. In many cases, it can be isolated simply by decantation of the reaction solvents and washed with an organic solvent such as chloroform to free it from unreacted starting materials. Where a water-miscible solvent is used, the solvent can be removed by distillation, the residue taken up in water, extracted with an organic solvent in which the starting materials are soluble and the aqueous solution freeze-dried. When a water-immiscible solvent is used, the reaction mixture can be treated with water, the aqueous layer separated and extracted with an organic solvent in which the starting materials are soluble and then the aqueous solution freeze-dried. In another modification of the invention, the quaternary ammonium compound can be purified or converted to the corresponding compound containing a different anion by passing an aqueous solution of the compound through an ion exchange column containing an ion exchange resin, eluting the quaternary ammonium compound with a dilute solution of the acid capable of furnishing the anion desired in the final substance and freeze drying the eluate.

The products of the invention can also be produced by reacting an amino ester of the formula,

NHC 0 CHCI:

Threo form where R, and R are the same or different and represent hydrogen or lower alkyl radicals such as methyl and ethyl radicals; with an alkylating agent. Preferred alkylating agents are the alkyl halides and, in the cases where R, and R represent lower alkyl radicals, dialkyl sulfates. Other alkylating agents, for example methyl benzenesulfonate and methyl p-toluenesulfonate, can also be used. The reaction is preferably carried out in a solvent using an excess of the alkylating agent. The reaction proceeds quite readily and hence high reaction temperatures need not be used. The ease of reaction varies with the alkylating agent employed. When alkyl halides are used, the iodides are preferred for small batches owing to the greater convenience of manipulation while for larger batches the cheaper bromides are preferred. As solvents, both watermiscible and water-immiscible inert organic solvents can be used. Some examples of such solvents are chloroform, acetonitrile and benzene. The product can be isolated from the reaction mixture by the methods described above.

Still another method for producing the compounds of the invention comprises reacting threo-l-p-nitrophenyl-Z- dichloroacetamidopropane-1,3-dial with a quaternary ammonium compound of formula (lower alkyl) sNOHzC 0 X-A- where X is a halogen and A- is a non-toxic anion. The reaction is preferably carried out in a basic reaction medium. Such a reaction medium can be composed solely of a tertiary amine such as pyridine, triethylamine or quinoline or it can be composed of an unreactive organic solvent containing a portion of a tertiary amine to act as the acid acceptor. Satisfactory results can also be obtained by the use of a neutral, unreactive solvent. The

desired product can be isolated from the reaction mixture by use of the methods described previously.

As indicated above, compounds of the present invention in which the anion of the quaternary ammonium salt is a non-toxic anion such as a sulfate or phosphate ion can also be prepared from a corresponding halide or other salt by ion interchange in an ion exchange reaction system. One method of accomplishing this is by using ion exchange resins. Anion and cation exchange resins may be employed. For example, with anion exchange resins, an aqueous solution of the quaternary ammonium halide is adjusted to a pH of 2 by means of the acid supplying desired non-toxic anion, the solution passed through a column of the anion exchange resin which is prepared by washing with a dilute aqueous solution of the same acid, the eluate treated with an ion exchange resin until a pH of approximately to 5.5 is reached and the filtrate freeze dried to obtain the pure product. When cation exchange resins are employed, an aqueous solution of the quaternary ammonium compound is passed through a column of the resin in the acid form. The column is then washed with a dilute solution of the acid supplying the desired non-toxic anion, the eluate adjusted to a pH of 5 to 5.5 by means of ion exchange resins and the residual solution freeze-dried to give the desired product.

The ion interchange reaction can also be accomplished by reacting the corresponding halide with an inorganic salt whereby an insoluble inorganic halide is precipitated. For example, reaction of the quaternary ammonium halide with silver sulfate in aqueous medium yields the corresponding quaternary ammonium sulfate and a precipifate of a silver halide.

The compounds of the invention per se lack antibiotic activity. However, they are highly soluble in water and upon parenteral administration of such solutions the prodnets are very rapidly converted by the living body to chloramphenicol or its optical recemate, respectively, which exert their well-known potent therapeutic actions. These properties coupled with the fact that their aqueous solutions are not highly acidic make the products especially useful for the production of injectable preparations. For example, D -threo 1 p nitrophenyl 2 dichloroacetamido 3 dirnethylaminoacetoxyprop-an 1- ol methobromide exhibits a water solubility greater than 1 g./ml. in comparison to 0.0025 g./ml. for chloramphenicol itself and, at a concentration of 200 mg./ml., gives a clear colorless solution having a pH of about 4.1 which can be adjusted to a pH of about 6.5 without the formation of a precipitate. This solution upon injection rapidly releases chloramphenicol.

The invention is illustrated, but not limited, by the following examples:

Example I l g. of anhydrous trimethylamine is added to a solution of 4 g. of D-threo-l-p-nitrophenyl-2-dichloroacetamido-3- chloroacetoxypropan-l-ol in 25 ml. of acetonitrile at C. The mixture is allowed to warm to room temperature and to stand for one and a half hours. The solvent is removed by distillation in vacuo and the colorless residue dissolved in water. The solution is extracted with ethyl acetate and the aqueous solution frozen. The water is removed from the frozen solution in vacuo to obtain the desired D-threo-1-p-nitrophenyl-2-dichloroacetamido- 3 dimethylaminoacetoxypropan 1 o1 methochloride as a hygroscopic granular solid:

A273 in ethanol, [a] +l8.8 (c.=5%, water).

The principal infrared absorption bands of the product are 2.9, 3.37, 5.66, 5.87, 6.53, 7.39, 7.83, 7.95 and 8.34 microns.

The D -threo 1 p nitrophenyl 2 dichloroacetamido 3 chloroacetoxypropan 1 -ol used as the starting material in the above procedure can be prepared by reacting 36.2 g. of chloroacetyl chloride with 97 g. of

chloramphenicol in 26 ml. of pyridine and 450 ml. of dioxane at 30 C. for about one and a half hours. The product is isolated by dilution of the mixture with 600 ml. of water, extraction with 600 ml. of ethyl acetate and evaporation of the ethyl acetate from the washed and dried extract. The product is an oil which crystallizes on standing. After recrystallization from chloroform the product melts at 103-106 C.

Eit....=252

A271 in ethanol.

Example 2 0.61 g. of trimethylamine in 30 ml. of chloroform is added to 3 g. of D-threo-l-p-nitnophenyl-Z-dichloroaeetamido-3-bromoacetoxypropan-1-ol in 50 ml. of chloroform at 30-35 C. A colorless syrup separates from the mixture immediately. The reaction mixture is allowed to stand for one 'hour and then diluted with water. The aqueous layer is separated and extracted first with ethyl acetate and then with ether. The aqueous solution is filtered, warmed to remove dissolved ether and then frozen. The ice is removed by sublimation in vacuo to obtain the desired D-threo-l-p-nitrophenyl-Z-dichloroacetanfido-S-dimethylaminoacetoxypropan-l-ol methobromide as a hygroscopic granular solid; M.P. 103-107 C.,

x275 in water, [a] +18 (c.=2%, water). The principal infrared absorption bands of the product are 3.0, 3.27, 5.67, 5.86, 6.21, 6.53, 6.7, 7.06, 7.38, 7.93, 8.31, 9.01, 9.33, 9.72, 10.32, 10.8, 11.52, 11.66 and 12.3 microns.

The D threo-l-p-nitrophenyl-2-dichloroacetamido-3- bromoacetoxypropan-l-ol used as a starting material in the above procedure can he prepared by the procedure described for the corresponding 3-chloroacetoxy compound in Example 1 by substituting 64.3 g. of bromoacetyl bromide for the 36.2 g. of chloroacety] chloride.

Example 3 1 g. of anhydrous trimethylamine is added to 4 g. of D-threo-1-p-nitrophenyl-2-dichloroacetamido-3-chloroacetoxypropan-l-ol in 25 ml. of acetonitrile at 10 C. and the mixture allowed to warm to room temperature. The reaction mixture is allowed to stand for one and a half hours and then the solvent removed by distillation in vacuo. The residue is dissolved in water and extracted first with ethyl acetate and then with ether. The aqueous solution is warmed to remove dissolved ether, cooled and poured into an ion exchange column containing the acid form of Dowex 50. The eflluent is discarded and the column treated with dilute sulfuric acid. The sulfuric acid eluate is adjusted to pH 5.5 by treatment with IR 45 resin in the basic form. The ion exchange resin is removed irom the solution, the aqueous filtrate frozen and the ice sublimed from the frozen mass in vacuo to obtain the desired D-threo-1-p-nitnophenyl-2-dichloroacetamido-3-dimethylaminoacetoxypropan-l-ol methosulfate.

Example 4 0.33 ml. of triethylamine is added to 1 g. of D-threo-lp nitrophenyl-2-dichloroacetamido 3 bromoacetoxypropanrl-ol in 10 ml. of acetonitrile and the mixture allowed to stand at room temperature for one and a half hours. The solvent is removed by distillation in vacuo and the residue dissolved in water. The solution is extracted first with ethyl acetate and then with ether. The aqueous solution is frozen and the ice sublimed from the frozen mass in vacuo to obtain the desired D-threo-l-pnitrophenyl-Z-dichloroacetamido 3 diethylaminoacetoxypropan-l-ol etho-bromide as a colorless solid;

Eif =lfi2 A274 in water, [cab l-[ 16 (c.=2%, water).

Example 5 1.4 g. of methyl iodide is added dropwise with stirring to a suspension of 2.16 g. of D-threo-1-p-nitrophenyl-2- dichloroacetamido-3-diethylaminoacetoxypropan-l*ol in 6 m]. of acetonitrile and the reaction mixture stirred for two hours at room temperature. The solvent is removed by distillation in vacuo and the residue taken up in water. The mixture is filtered, the filtrate extracted with ether and the aqueous phase frozen. The ice is sublimed from the frozen mass to obtain the desired D-threo-bpmitrophenyl-Z-dichloroacetamido 3 diethylaminoacetoxypropan-l-ol m-ethiodide, [aj -l- 17 (c.=2%, water).

The D-threo-1pnitrophenyl-Zdichloroaoetamido-B-diethylaminoacetoxyprop-an-l-ol starting material can be prepared by allowing a solution of 9.3 ml. of diethylamine and 14 g. of D-threo-l-p-nitrophenyl-2-dichloroacetamido- 3-bromoacetoxypropan-1-ol (prepared from chlorampheniool and bromoacetyl bromide in the presence of pyridine) in 150 m1. of chloroform to stand for about twenty hours at room temperature, evaporating the mixture in vacuo, dissolving the residue in dilute hydrochloric acid, extracting the solution with ethyl acetate and basifying the aqueous solution with sodium bicarbonate. The gummy product crystallizes on standing; M.P. 108-l10 C.

By substituting methyl bromide for the methyl iodide and by substituting D-threo-l-p-nitrophenyl-2-dichloroacetamido-3-dimethylaminoacetoxypropan-l-ol for the D- threo-l-p-nitrophenyl-Z-dichloroaeetamido 3 diethylaminoacetoxypropan-l-ol in the above procedure one obtains D-threo-1-p-nitrophenyl-2-dichloroaoetamido-3-dimethylarninoacetoxypropan-l-ol methobrornide.

Example 6 1.9 g. of dimethyl sulfate dissolved in ml. of chloroform is added slowly to 4.32 g. of D-thrco-l-p-nitrophenyl 2 dichloroacetamido 3 diethylaminoacetoxypro-pan-l-ol in 150 ml. of chloroform and the resulting mixture allowed to stand at room temperature for two hours. Water is added to the reaction mixture and after thorough mixing the phases are separated. The chloroform phase is discarded and the aqueous phase extracted first with ethyl acetate and then with ether. The dissolved ether is removed from the aqueous phase in vacuo and the solution passed through a column of Dowex 50 in the acid form. The efliuent is discarded and the column treated with dilute sulfuric acid. The sulfuric acid eluate is collected, the pH adjusted to 5.5 with IR 45 resin in the basic form and the resin removed by filtration. The filtrate is frozen and the ice sublimed in high vacuo to obtain the desired D-threo-l-p-nitrophenyl-Z-dichloroacetamido-3-diethylaminoacetoxypropan-l-ol methosulfate.

D-threo-l'p-nitrophenyl-2dichloroacetamido-3-dimeth ylaminoacetoxypropan-l-ol methosulfate can be prepared by substituting D-threo-l-p-nitrophenyl-Z-dichloroacetamido-3-dimethylaminoacetoxypropan-l-ol for the D-threol-p-nitrophenyl-2-dichloroacetamido-3 diethylaminoacetoxypropan-l-ol used in the above procedure.

Example 7 5.13 g. of (chloroformylmethyl)trimethylammonium chloride is added portion-wise to a stirred solution of 9.7 g. of DL-threo-l-p-nitrophenyl-2-dichloroacetamido-propane-1,3-diol, 5.2 ml. of dry pyridine and 250 ml. of chloroform and the mixture allowed to stand at room temperature for fifteen hours. The reaction mixture is diluted with water and the organic phase discarded. The aqueous phase is extracted first with ethyl acetate and then with ether. The dissolved ether is removed from the aqueous solution in vacuo and the solution passed through a column of Dowex 50 resin in the acid form. The effluent is discarded. The column is treated with dilute sulfuric acid and the eluate collected. The eluate is adjusted to pH 5 to 5.5 with IR 45 resin in the basic form. The resin is removed by filtration and the filtrate frozen.

The ice" is sublimed from the frozen mass to obtain the desired DL-threo1-p-nitrophenyl-2-dichloroacetamido-3- dimethylaminoacetoxy-propanl-ol methosulfate.

By substituting dilute hydrochloric acid or dilute hydrobromic acid for the sulfuric acid used in the elution of the Dowex 50 column one obtains DL-threo-l-p-nitrophenyl- 2-dichloroacetamido-3-dimethylaminoacetoxy-propan-l-ol methochloride and DL-threo-l-p-nitrophenyl-Z dichloroacetamido-3 dimethylaminoacetoxypropan l ol methobromide, respectively.

Example 8 l g. of D-threo-1-p-nitrophenyl-2-dichloroacetamido-3- dimethylaminoaoetoxypropan-l-ol methobromide is dissolved in L0 ml. of water and the pH of the solution adjusted to 2 with dilute sulfuric acid. The solution is passed through a column containing an anion exchange resin IRA 410 previously washed with dilute sulfuric acid to produce the sulfate form. The eluate from the column is treated with IR 45 resin in the basic form until the pH is approximately 5 to 5 .5. The ion exchange resin is removed and the filtrate frozen. Sublimation of the ice from the frozen mass in vacuo yields the desired D-threol-p-nitnophenyl-Z dichloroacetarnido 3 dimethylaminoacetoxypropan-l-ol methosulfate.

Example 9 1 g. of D-threo-l-p-nitrophenyl-2-dicholoracetamido-3- dimethylaminoacetoxypropan-l-ol methobromide is dissolved in 10 ml. of water and the resulting solution passed through a column containing 3 ml. of Dowex 50 in the acid form. The efliuent is discarded and the column treated with dilute sulfuric acid. The sulfuric acid eluate is collected, the pH adjusted to about 5 to 5.5 with IR 45 resin in the basic form and the resin removed by filtration. The filtrate is frozen and the ice sublimed from the mass in vacuo to obtain the desired D-threo-l-p-nitrophenyl-2- dichloroacetarnido 3 dimethylaminoacetoxypropan-l-ol methosulfate.

The ion exchange resins mentioned in the above examples are described in more detail in Calmon and Kressman, Ion Exchangers in Organic and Biochemistry," Interscience Press, 1957, New York, New York.

We claim:

1. A compound having the structural formula NBC 0 CH 01:

wherein A is a non-toxic inorganic anion.

2. A compound having the structural formula NH 0 0 0110b omQ-o HOH(JH-CH:O C 0 01-bit (lower elkylh-X- Three form wherein X- is a halide ion.

3. Three l p nitrophenyl -2-dichloroacetamido-3-dimethylaminoacetoxypropanl-ol methohalide.

4. D threo 1 p nitrophenyl-2-dichloroacetamido-3- dimethylaminoacetoxypropan-l-ol methobrornide.

5. D threo l p nitrophenyl-Z-dichloroaoetamido-S- dimethylaminoacetoxypropan-1-ol methochloride.

6. Threo-l-p-nitrophenyl 2 dichloroacetamido-3-diethylaminoacetoxypropan-1-01 ethohalide.

7. D threo l p nitrophenyl-2-dichloroacetamido-3- diethylaminoacetoxypropan-l-ol ethobrornide.

8. Threo 1 p nitrophenyl 2 -dicholoroacetamido-3- diethylaminoacetoxypropan-l-ol methohalide.

9. D threo l p nitrophenyl-Z-dichloroacetamido-3- diethylaminoacetoxypropan-l-ol methiodide.

10. D threo 1-p-nitrophenyl-2-dicholoroacetamido-3- dimethylaminoacetoxypropan-l-ol methosulfate.

11. A compound having the formula of claim 1 in which A- is the anion of an acid of the class consisting of 7 hydrochloric, hydrobu'omic, hydroiodic, sulfuric and phoephoric.

References Cited in the file of this patent UNITED STATES PATENTS 0 2,102,103 Urbain et a1 Dec. 14, 1931 2,359,862 Linch Oct. 10, 1944 2,616,922 Ringwald et a! Nov. 4, 1952 8 OTHER REFERENCES Sidgewicks Onganic Chemistry of Nitrogen (1949), p.

1002 (Aug. 9, 1958). 

1. A COMPOUND HAVING THE STRUCTURAL FORMULA
 10. D - THREO - 1-P-NITROPHENYL-2-DICHOLORACETAMIDO-3DIMETHYLAMINOACETOXYPROPAN-1-OL METHOSULFATE. 